Losing 15lbs before August 20th?

So I amm 14 (15 on Monday!), and I would like to lose about 15 lbs for my cousin's wedding on August 20th. Not only do I want to do this, but also get rid of my acne! How long should I run for to gain my goal, while eathing healthy and drinking plenty of water? I have bumbbells, but I can't go to the gym. Incase you're wondering, I am 5'7 and 140 lbs. Thank you!